1. Field of the Invention
The present invention relates to apparatus for vehicle surroundings monitorings that assists in the checking of the periphery of a vehicle by its passenger by displaying images of the periphery of the vehicle captured by vehicle-mounted cameras.
2. Background Art
There is known a method for assisting parking operations after automatically recognizing a parkable parking space and detecting the condition of the periphery by, in parking a vehicle in a parking lot, recognizing white lines drawn on a road surface or spaces that are not occupied by other vehicles.
For example, there has been proposed a parking aid device comprising: a steering state detection means that detects the steering state of a vehicle; a parking space detection means that detects a parking space through image recognition based on an image from a camera; an predicted path of the vehicle computation means that computes an predicted path of the vehicle based on information from the steering state detection means; and notification means that provides to the driver information that aids parking based on information on the predicted path of the vehicle and the parking space (for example, see JP Patent Publication (Kokai) No. 11-339194 A (1999) (Patent Document 1)).
In addition, in recent years, there has been proposed a technique in which, with a view to finding the relative positions of a vehicle and a parking space with ease during parking operations, images from plural vehicle-mounted cameras are combined to create a bird-viewimage comparable to one that might be taken from right above the vehicle.
However, in creating a single bird-view image by compositing plural images captured by plural vehicle-mounted cameras, there is a problem in that brightness and contrast cannot be adjusted appropriately between each two cameras or within the images by each of the vehicle-mounted cameras, and the observed image of targets is not easy to recognize. For example, it is often the case that while a given vehicle-mounted camera may be capturing clear and easy to view images, another vehicle-mounted camera may be facing the sun, while yet another vehicle-mounted camera may be in the shade of a nearby vehicle. Further, since the direction of each vehicle-mounted camera is often uncontrollable and fixed, the state of the objects being shot by each camera changes from moment to moment with the ups and downs of the road, the direction of travel, changes in the weather, etc., and the images captured by each of the vehicle-mounted cameras, too, will vary randomly in their luminance and color balance from moment to moment.
As techniques for compositing images captured by plural cameras, JP Patent No. 3297040 B1 (Patent Document 2) and JP Patent Publication (Kokai) No. 2004-96488 A (Patent Document 3) are known, for example. Patent Document 2 discloses a technique in which tone correction is performed based on the brightness value average of overlapping areas among images captured by plural vehicle-mounted cameras. The object of the technique disclosed in Patent Document 2 is to generate an image with a wide dynamic range and good visibility by capturing images with varying exposure amounts while the vehicle is moving, and compositing the thus captured plural images after they have undergone bird-view conversion.
Further, there is disclosed in Patent Document 3 a technique in which images are composited by extracting from images captured by plural cameras partial images with appropriate exposure amounts. The object of the technique disclosed in Patent Document 3 is to generate a composite image that is easy to view by extracting, from plural images which are of the same area and taken using plural imaging devices with varying exposure amounts, images that each have an appropriate exposure amount.